Pollulant containment system

ABSTRACT

A pollutant containment system for containing the spillage of fuels or other hydrocarbons or the like comprises a first layer ( 14, 60 ), a containment vessel ( 16 ) for receiving liquid passing through the layer ( 14 ) and channelling means ( 22 ) for directing liquid permeating through the layer towards the containment vessel ( 16 ). The layer ( 14 ) provides a plurality of active surfaces for the retention of pollutant and is such as to cause water to permeate through the layer at a flow rate to avoid emulsification of oil and water. Water is introduced into and removed from the containment vessel to raise and lower the water surface thereby to cause the pollutant to be smeared over the active surfaces.

The present invention relates to a pollutant containment system.

In some situations—refuelling stations, chemical loading bays, surfacedrainage systems and vehicle parks, for instance—there may be risk ofspillage of fluids such as fuel oils and other hydrocarbons. These mustbe prevented from entering the drainage system and so passing byuncontrolled discharge into the environment, and must be prevented fromentering the environment at all without preliminary treatment.

Where there are large areas of conventional, impermeablepavement—motorways, for instance—flash storms may cause such floodingthat existing storm-water provisions become overloaded. There have beenoccasions, too, when emergency treatment of spillage after accidentsinvolving chemical tankers has resulted in serious damage to theenvironment over wide areas.

Where risks of chemical contamination are low, various forms of porouspavement have been employed, allowing spillage to soak away into theground beneath. There is, however, a limited rate at which ground canabsorb moisture, and there remains a risk of flooding when rainfall isvery high. Pollutant containment systems are known which have an uppersurface permeable to liquid in order to allow pollutants such as oils topass through the surface. However, a difficulty with conventionalsystems is that they do not provide adequate protection to surface andgroundwater and the surrounding area in the event of a major leak suchas might result from a sump or fuel tank failure from a vehicle or aleakage from a ruptured drum.

The term “pavement” is used herein in its international sense to mean,inter alia, a covering for a street, roadway or other large surface areaand particularly such areas which are designed to support repeatedvehicular loading.

The term “face velocity” is used herein to refer to the speed at whichwater passes through the first layer of the system.

The term “pollutant” used herein refers primarily to fuel oils and otherhydrocarbons, and includes a mixture of liquid and solids where thesolids are held in suspension.

The present invention seeks to provide an improved pollutant containmentsystem.

Accordingly, the present invention provides a pollutant containmentsystem comprising:

-   -   a first layer; containment means for receiving water and liquid        pollutant passing through said layer; and channelling means for        directing water permeating through said layer towards said        containment means; wherein said layer provides a plurality of        active surfaces for the retention of pollutant and is such as to        cause said water to permeate through said layer at a flow rate        less than that which would give rise to emulsification of said        pollutant.

In a preferred form of the invention said containment means isimpermeable to water. It has an upper opening for receiving said liquidand said channelling means extends vertically over said opening therebyto direct liquid permeating through said layer into said containmentmeans. Said channelling means extends into said opening below an upperedge thereof and is generally foil-shaped.

Advantageously, said channelling means has an upper edge extending alonga periphery of said first layer. Filter means are provided extendingfrom a side wall of the containment means for filtering liquidoverflowing from said containment means. In situ, said containment meansrests on a ground surface and said filter means allows infiltration ofliquid into the ground. Preferably, said containment means is containedwithin said layer. Said first layer is formed of particulate materialand the surfaces of particle of said particulate material form saidactive surfaces. At least a portion of said layer may be formed by apolarity of storage elements, each of which has an internal structureproviding said active surfaces.

Advantageously, a containment wall extending around the perimeter ofsaid first layer.

Said filter means extends from an upper edge of a side wall of thecontainment means towards an upper surface of said first layer.Preferably, said filter means extends to said containment wall. In oneembodiment, at least one of said channelling means and said containmentmeans is formed by a substantially non-permeable material which may be ageo-membrane. Ideally, said geo-membrane is covered with a geo-textilematerial.

The system may also include inlet means for introducing water into saidcontainment means, the inlet means comprising at least one pipe.

The present invention also provides a method of containing the spillageof fuels or other hydrocarbons or the like in a system according to theinvention comprising introducing water into said containment meanswhereby pollutant floats on the surface of said water and is retained insaid layer on said active surfaces thereby to enable biodegradation ofsaid pollutant.

In a preferred method water is introduced into and removed from saidlayer to raise and lower the water surface thereby to cause saidpollutant to be smeared over said active surfaces. Preferably, saidwater is introduced into and removed from said containment vessel. Themethod may also comprise introducing nitrogen and/or phosphorouscompounds into said layer to assist biodegradation of said pollutant.

The present invention allows the safe installation of pollutantcontainment systems where there is a risk of non-aqueous phasepollutants, primarily oils, leaking into the environment.

The present invention is further described hereinafter, by way ofexample, with reference to the accompanying drawings, in which:

FIG. 1 is a part cross-sectional view of a preferred form of pollutantcontainment system according to present invention;

FIGS. 2 to 6 are views, similar to that of FIG. 1, showing furtherembodiments of pollutant containment systems according to the presentinvention.

Referring to FIG. 1, this shows a cross section through a preferred formof pollutant containment system 10 which has a first, substrate layer 14supporting an upper, surface layer 12.

As can be seen from the drawing, the substrate 14 is laid in a ‘well’ 11which can be excavated in the ground 13 or formed in some other way, forexample by retaining walls permeable to water. In the example shown, thewell is formed by excavating the ground to the required depth.

The surface layer 12 is a porous layer which is permeable to liquid andforms the pavement. It may be a single sheet laid or cast over the wholeof, or a large section of, an area, in which the perforations mayconveniently be simple holes. However, it is advantageous to have holesof small span to stop ingress of foreign objects, but of long peripheryto facilitate dispersion of the fluid underneath the pavement. Slot-likeholes are therefore attractive, and these can conveniently be providedby grooves on the outside of prefabricated pavings.

In a further preferred arrangement, the layer 12 may be formed bydiscrete pavings of such size and mass as to be convenient to handlecontinually without fatigue, and designed to be laid close-fittingwithout mortar or cement. They may be made in any material suitable forany particular application, such as brick, concrete, or cast iron, andmust be of sufficient depth to ensure dispersion of the concentratedloads applied. The perforations may be conveniently formed by, forexample, gaps between adjacent edges of the paving blocks. The layer 12may be made of porous concrete or porous asphalt.

The substrate layer 14 is of particulate material whose particles may benon-uniform in shape and which provide interstices between theparticles. A typical particle size is in the range 10 mm to 50 mm andthe particles may be of mixed sizes. The surface of the particles forman “active” surface over which pollutant can be smeared as it passesthrough the layer 14, to allow time for biodegradation of the pollutant.

A containment vessel 16 is provided within the substrate layer 14,although it could, of course, be located beneath the substrate layer aspart of a containment wall for the substrate layer. The containmentvessel 16 is shown as having a base 18 and side walls 20 which extendgenerally vertically or near vertically from the base 18 (although theymay extend at any suitable angle) to form an upper opening or mouth forthe vessel. The containment vessel 16 can be of any suitable shape, forexample, rectangular or circular of even of ‘saucer’ shape where thewalls and base may merge into one.

The containment vessel 16 should be of sufficient size to contain thelevel of pollutant which might be expected to be discharged from a majorleak from, for example, a sump or fuel tank of a vehicle or from aruptured drum.

The system also has a channelling means in the form of a secondcontainment vessel 22. This is of funnel-shape and extends from thepavement layer 12 into the first containment vessel 16. The containmentvessel 22 has a lower end region in the form of a mouth or openingformed by a lower edge 24 which lies below the mouth of the containmentvessel 16. The containment vessel 16, in effect, forms an artificialwater table and ideally the lower edge of the second containment vessel22 extends below the mouth of the first containment vessel 16 by anamount sufficient to allow the level of the water in the containmentvessel 16 to rise and fall by a reasonable amount without falling belowthe mouth of the vessel 22 or rising above the mouth of the vessel 16.Pollutants which are lighter than water will float on the surface of thewater and the effect of the raising and lowering of the water level isto ‘smear’ these pollutants over the active particle surfaces of thesubstrate. The pollutant can then be acted on by aerobic bacteria which,with the addition of suitable amounts of, for example, nitrogen andphosphorus, can develop on the surface of the substrate material.

The water level can be raised and lowered artificially by introducing itinto the material 14 through pipes or the like which extend into thevessel 16 or the material 14 outside the vessel 16 or both. The watercan also be introduced at the upper surface of the layer 14 or layer 12or into an upper region of the layer 14. The raising and lowering of thewater level pushes carbon dioxide out of the material 14 and introducesoxygen to assist in the biodegradation of the pollutants.

Pollutants which are heavier then water will sink to the bottom of thevessel 16 and can be removed at some later date.

Both of the containment vessels 16 and 22 are formed of waterimpermeable material and preferably of oil resistant material. Each maybe made from a polymeric geomembrane of welded construction which iscovered on both sides with a geotextile material 23 to protect thegeomembrane from the substrate material. The containment vessels mayalso be made of, for example, moulded plastics material. The arrangementof the two containment vessels 16, 22 enables a first vessel 16 to beused which can be considerably smaller than the area to be protected bythe system. The second vessel 22 can be used to direct pollutants intothe vessel 16 from a larger area than the area immediately above thevessel 16.

A containment wall 26 may be provided, extending around the perimeter orperipheral edge of the pavement layer 12, to provide a water impermeablebarrier which contains any spillage of pollutant within the perimeter ofthe pavement layer 12. The second containment vessel 22 may extendeither directly from the junction of the containment wall 26 with thepavement layer 12 or from a point on the inner surface of thecontainment wall 26 at a level below the pavement layer 12. This ensuresthat all of the water and pollutant which passes through the porouspavement layer 12 is directed by the second containment vessel 22 intothe first containment vessel 16.

The first containment vessel 16 may also be connected to the containmentwall 26 by way of a further filter layer 28. This filter layer 28 can bein the form of a geotextile or other filter material. If the vessel 16overflows, the filter layer 28 allows the overflow water to pass throughit and into the surrounding area and eventually to a nearby drain whilstpreventing the passage of pollutants. The filter layer can extend fromthe upper edge or mouth of the first containment vessel 16 to thecontainment wall 26 and thus provides a space between the filter layer28 and the second containment vessel 22 in which pollutants can betrapped if the containment vessel 16 overflows. The biologicaldecomposition of the pollutants in this space can be enhanced byintroducing nitrogen or phosphorus rich material such as fertilizer intothis gap.

An access means such as one or more access or recovery wells 30 isprovided to enable an assessment to be made of the water level in thefirst containment vessel 16. The access well 30 is typically acylindrical pipe extending from the pavement layer 12 through thesubstrate 14 and ending close to the bottom of the first containmentvessel 16. The pipe is open at each end and over most of its length fromits lower end is provided with openings through which the water andpollutants can freely pass. The upper end of the pipe 30 can be coveredwith an access plate or cover which allows ready inspection of theinterior of the pipe 30. The access well 30 also allows quick and easyremoval of excess water and pollutants from the containment vessel 16using, for example, a skimmer pump.

A discharge pipe or pipes (not shown in the drawing) can additionally oralternatively be connected to the first containment vessel 16, openinginto the vessel at a position which is normally below the water levelbut above the normal depth of solid pollutants at the bottom of thevessel 16 in order to enable excess water to be drawn off.

As is mentioned above, enhanced bioremediation may be effected byraising and lowering the surface of the water retained in thecontainment vessel 16 in order to cause the pollutants which float onthe surface of the water to be smeared over the particulate material ofthe substrate 14. This raising and lowering of the water level can beeffected artificially by introducing water and removing it or byallowing rainwater to accumulate and dissipate. Suitable amounts ofnitrogen and phosphorous compounds can be introduced either through theporous pavement layer 12 or through various access means into the gapbetween the filter layer 28 and the second containment vessel 22 toassist biodegradation.

In use, if a large spill of, for example, oil were to take place on theporous pavement 12, this would pass through the pavement 12 and into thesubstrate 14 and would be directed towards the containment vessel 16 viathe second containment vessel 22 in order to prevent it infiltratingdirectly into the surrounding ground.

If water were to pass rapidly through the substrate, for example as aresult of heavy rainfall or the spraying of water onto the upper surfacelayer 12, the oil on the active surfaces would be captured by the waterand would become emusified making separation of the oil and water verydifficult, if not impossible, in the system. However, the nature of thesubstrate means that the water permeates through the substrate with avery low face velocity i.e. at a flow rate which is low enough to avoidemulsification of the oil taking place. As a result, the oil and waterremain separated in the substrate. The irregular nature of the shape ofthe particulate material used in the substrate 14 and the resultingformation of interstices within the substrate means that the pathfollowed by oil and water droplets as they permeate through thesubstrate is significantly greater than would otherwise be the case.

Pollutants which float on the surface of the water would be ‘smeared’over the particulate material of the substrate for biodegradation. Anyoverflow from the containment vessel 16 would be trapped by the filterlayer 28 for further biodegradation. Heavy pollutants which sink to thebottom of the containment vessel 16 can be removed by way of the accesswell 30, if necessary, as can excess water. In the illustrated exampleof FIG. 1, water infiltrates into the surrounding ground 13 afteroverflowing from the vessel 16 and the provision of one or moredischarge pipes can assist in the water removal from the vessel 16.

FIG. 2 is a view to that similar to that of FIG. 1 showing a secondembodiment of pollutant containment system according to the presentinvention. Parts of FIG. 2 corresponding to parts in FIG. 1 are givenlike reference numbers.

Whilst the system of FIG. 1 is intended to be more or less a permanentstructure with a load bearing upper surface layer 12, the system of FIG.2 may be used in situations where a temporary structure is required.This could be, for example, during building construction in areas wherethe constructors vehicles are parked or are driven.

In the system of FIG. 2 the layer 12 is omitted and the substratematerial 14 provides the upper, load-bearing surface. The containmentvessel 16 is located within well 11 which has been excavated in theground. It will, of course, be appreciated that the well 11 couldequally be formed by a structure which has been built for the purpose.

The containment vessel 16 is of generally rectangular or square shapeand has a base 18 with three side walls 20 extending to the groundsurface 15. The three side walls 20 conveniently lie against or adjacentside walls of the well 18. However, the fourth wall 40 of the vessel 16is spaced from the adjacent side wall of the well and terminates in anupper edge 42 which is well below the ground surface 15. The secondcontainment vessel 22 has a generally vertical wall 44 which extends thefull depth of the well 11. In the example of FIG. 2 this wall is steppedat 46 but this is not essential.

The vessel 22 also has a generally horizontal base 23 which overlies thewall 40 of vessel 16 and has a depending wall 50 extending into thecontainment volume of the vessel 16 but which terminates above the base18 of the vessel 16.

The wall 44 forms the fourth wall of the containment system 10 andconnects with the two adjacent walls 20 of the vessel 16. The extension48 also extends the full length of the wall 44, as does the wall 50.

The whole of the volume within the well is filled with the particulatematerial 14.

The arrangement of the vessels 16 and 22 is such that the latter directsflow of liquid (water and pollutants) percolating through the material14 into the vessel 16. The side walls 20 and 44 prevent any spillage onthe material 14 from infiltrating directly into the surrounding ground.

In addition, a layer 47 of geotextile material covers the upper surfaceof the base 23 and may extend across the vessel 16 to the opposite wall20 to act as a filter.

A further layer 49 of geotextile material also covers the undersurfaceof the base 23 and extends along the surface of the wall 50 to the base18 where it extends to the walls 20.

The bottom of the well between the wall 40 and the wall 44 is covered bya geotextile material layer 51 to allow infiltration of water from thematerial 14 into the ground. Additionally or alternatively, one or morepipes or other conduits can be used to carry water away from the volumebetween the walls 44 and 40. A perforated pipe or conduit extending intothe volume between the walls 44 and 40 would be suitable. The same pipescould be used to introduce water.

The geotextile layers serve as filters and also to protect the surfaceof the vessels 16, 22 where the layers are provided. They may of coursebe of any suitable material and not necessarily geotextile material.

The system of FIG. 2 operates in the same manner as the system ofFIG. 1. Pollutant and water separate as they pass slowly through thematerial 14. The water fills the vessel 16 and overflows the wall 40 toinfiltrate into the ground through the layer 51. The layers 47, 49 and51 provide additional filtering for the water.

Referring now to FIG. 3, this is a system similar to that of FIG. 2 butwhich has an upper, load-bearing layer 12 as in the system of FIG. 1.The arrangement of the vessels 16 and 22 and the geotextile layers isthe same as in FIG. 2 but the “substrate” is formed by two layers. Thefirst is formed by the particulate material 14 which supports the layer12 and lies between the layer 12 and the geotextile layer 47. The secondlayer is formed by what are termed hollow storage elements 60 which fillthe volume beneath the base 23 and the geotextile layer 47.

The storage elements 60 are generally made of plastics material and areof regular shape (typically square or rectangular cross section). Theyhave an internal structure which provides a plurality or myriad oftortuous or winding paths between upper and lower surfaces for the waterand oil to percolate slowly through the structure, ensuring a low facevelocity and thus separation of the pollutant and water. The internalstructure of the storage elements 60 may, for example, be in the form ofsmall, interconnected cavities, or a latticework. The elements 60 may becommercial “plastic honeycomb” systems and one such element is a boxstructure known as “Permastore”. The elements provide the “active”surfaces on the internal walls of the cavities and interstices formedwithin the elements.

The system of FIG. 4 is similar to that of FIG. 3 with the exceptionthat a further layer of particulate material 14′ is provided beneath thebase 18 of the vessel 16 and the geotextile layer 51. This additionallayer 14′ serves as a supporting layer and allows water permeatingthrough the geotextile layer 51 to flow laterally and infiltrate theground over a wider area. This enables the water to be conducted awayfrom the layer 51 more quickly, allowing the system to cope with largervolumes of water.

FIG. 5 is a system similar to that of FIG. 3. However, in FIG. 5 theupper surface layer 12 is again omitted. In addition, the geotextilelayer 47 is omitted and one or more of the storage elements 60 arereplaced with particulate material 14. In the illustrated example, oneor more of the storage elements 60 in the volume bounded by the walls 20and 50 are omitted but any one or more of the storage elements can bereplaced by material 14.

The system of FIG. 6 is a system similar to that of FIG. 2 but with theparticulate material 14 replaced by layers formed by storage elements60.

The above described embodiments can be strong enough for vehicularloading and can therefore be used in, for example, permanent ortemporary car and goods vehicle parks. However, they can also be used inareas which are not intended to take vehicles. One example would be anarea where one or more fuel tanks are stored for providing fuel for, forexample, heating or generators.

It will be appreciated that various combinations of the systems shown inFIGS. 1 to 6 can be used and features of the various embodiments can becombined with one another.

The size of the above-described system is determined by the amount ofpollutant (oil) retention that will be required from the predicted spillthat might take place, and also to ensure sufficient depth such that thewater in the vessel 16 is protected from freezing in winter. The firstcontainment vessel 16 is conveniently positioned at a sufficient depthto avoid freezing and minimising evaporation of the water in thecontainment vessel.

The above-described system avoids the extra cost of an additional oilinterceptor and can trap large amounts of pollutants without the risk ofthe surrounding area or drainage systems being contaminated. The systemprovides protection from spillages until the design volume is exceeded.Ideally, the system is constructed in order to maintain a permanentlevel of water in the containment vessel 16.

It will be appreciated that the vessel 22 can, as described, extend thefull width of the vessel 16 or only a portion. In the latter case thevessel 16 will have additional side walls 20 meeting the wall 44 and thevessel 16 will be shaped accordingly.

It will also be appreciated that the above described containment systemsare self contained in that they are intended to contain any spillage onthe upper surface of the system and to this end are provided with waterimpermeable barriers or retaining walls around the system.

Each vessel 16 and 22 can be constructed from component parts forassembly on site. They can also be constructed from, for example,concrete or other building material with a water impervious coating orlayer attached, or a substantially non-permeable material such as ageomembrane.

Where the well 11 is formed by a retaining wall then there would need tobe provision made for the infiltration of water into the surroundingground. This could be effected by way of the aforementioned dischargepipes but equally the wall could be porous.

1. A pollutant containment system comprising: a first layer (14, 60);containment means (16) for receiving water and/or oil passing throughsaid layer (14); and channelling means (22) for directing said waterand/or oil permeating through said layer towards said containment means(16); wherein said layer is formed of a material having intersticesproviding a plurality of winding paths throughout said layer (14, 60)thereby to cause said water and/or oil to permeate slowly through saidlayer at a flow rate below which emulsification of water and oil takesplace; and the surface of said material serves as a plurality of activesurfaces for the retention of oil smeared thereon.
 2. A system asclaimed in claim 1 wherein said containment means (16) is impermeable towater.
 3. A system as claimed in claim 1 wherein said containment means(16) has an upper opening for receiving said liquid and said channellingmeans (22) extends vertically over said opening thereby to direct liquidpermeating through said layer into said containment means (16).
 4. Asystem as claimed in claim 3 wherein said channelling means extends intosaid opening below an upper edge thereof.
 5. A system as claimed inclaim 3 wherein said channelling means (22) is generally funnel-shaped.6. A system as claimed in claim 1 wherein said channelling means (22)has an upper edge extending along a periphery of said first layer (14).7. A system as claimed in claim 1 further comprising filter means (28,51) extending from a side wall of the containment means (16) forfiltering liquid overflowing from said containment means.
 8. A system asclaimed in claim 7 wherein, in situ, said containment means (16) restson a ground surface and said filter means (28, 51) allows infiltrationof liquid into the ground.
 9. A system as claimed in claim 1 whereinsaid containment means (16) is contained within said layer (14).
 10. Asystem as claimed in claim 1 wherein said first layer (14) is formed ofparticulate material and the surfaces of particle of said particulatematerial form said active surfaces.
 11. A system as claimed in claim 1wherein at least a portion of said layer (14) is formed by a polarity ofstorage elements, each of which has an internal structure providing saidactive surfaces.
 12. A system as claimed in claim 1 comprising acontainment wall extending around the perimeter of said first layer(14).
 13. A system as claimed in claim 7 wherein said filter means (28)extends from an upper edge (42) of a side wall (40) of the containmentmeans (16) towards an upper surface of said first layer (14).
 14. Asystem as claimed in claim 7 wherein said filter means (28) extends tosaid containment wall.
 15. A system as claimed in claim 1 wherein atleast one of said channelling means (22) and said containment means (16)is formed by a substantially non-permeable material.
 16. A system asclaimed in claim 15 wherein said material is a geomembrane.
 17. A systemas claimed in claim 16 wherein said geo-membrane is covered with ageotextile material.
 18. A system as claimed in claim 1 comprising inletmeans for introducing water into said containment means (16). 19 Asystem as claimed in claim 18 wherein said inlet means comprises atleast one pipe.
 20. A system as claimed in claim 1 comprising accessmeans (30) extending through said layer (14) into said containment means(16) for enabling removal of water or surface pollutant directly fromsaid containment means.
 21. A system as claimed in claim 20 wherein saidaccess means is a pipe.
 22. A method of containing the spillage of fuelsor other hydrocarbons or the like in a system as claimed in any of thepreceding claims comprising introducing water into said containmentmeans (16) whereby pollutant floats on the surface of said water and isretained in said layer (14) on said active surfaces thereby to enablebiodegradation of said pollutant.
 23. A method as claimed in claim 22further comprising introducing and removing water into and from saidlayer to raise and lower the water surface thereby to cause saidpollutant to be smeared over said active surfaces.
 24. A method asclaimed in claim 23 wherein said water is introduced into and removedfrom said containment vessel (16).
 25. A method as claimed in claim 22,further comprising introducing nitrogen and/or phosphorous compoundsinto said layer (14) to assist biodegradation of said pollutant.
 26. Amethod as claimed in claim 22 wherein said water is introduced into anupper region of said layer
 14. 27. A method of containing the spillageof fuels or other hydrocarbons or the like comprising providing a systemas claimed in claim 1, and introducing water into said layer 14 to causepollutant to float on the surface of said water and thereby to beretained in said layer (14) on said active surfaces to enablebiodegradation of said pollutant.